1. Field of the Invention
The present invention relates to a small watercraft. More particularly, the present invention relates to a structure of an oil return port from an oil separator of a breather mechanism of an engine to an oil tank.
2. Description of the Related Art
In recent years, so-called jet-propulsion personal watercraft, which are one type of small watercraft, have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a bottom hull surface and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.
In the personal watercraft, a multiple-cylinder engine is mounted such that a crankshaft extends along the front-rear direction of a body of the watercraft. In the multiple-cylinder engine of a wet-sump type, an oil tank is provided on a bottom portion of a crankcase to be integral with the crankcase to allow the oil tank and the crankcase to have a common chamber, and therefore the oil tank is elongate in the front-rear direction of the body. On the other hand, in the multiple-cylinder engine of a dry-sump type, a chamber of the oil tank is formed to be independent of a chamber of the crankcase, and, when the oil tank is provided below the engine, the oil tank is elongate in the front-rear direction of the engine. In both engines, lubricating oil inside the oil tank is fed to components of the engine that require lubrication by using a feed pump or the like.
In these engines, with reciprocation of a piston and by a blow-by gas from a combustion chamber, a pressure inside the crankcase varies. In order to inhibit the reciprocation of the piston of the engine from being impeded due to a variation in the pressure, it is required that the crankcase communicate with an ambient side to allow the variation in the pressure of the crankcase to be lessened.
More specifically, the crankcase communicates with the ambient side through a breather pipe, or the crankcase communicates with a cam chamber of a cylinder head through a cam chain tunnel and the cam chamber communicates with the ambient side through the breather pipe to allow the variation in the pressure of the crankcase to be lessened. In this case, the breather pipe communicates with, for example, an air cleaner box.
Meanwhile, a chamber of the crankcase or a cam chamber communicating with the chamber of the crankcase through a chain tunnel is full of oil mist. In order to inhibit a blow-by gas containing the oil mist from flowing into the air cleaner box through the breather pipe, a breather mechanism is typically provided with an oil separator for separating the oil mist from the blow-by gas. The blow-by gas from which the oil has been separated within the oil separator, is drawn into the air cleaner box through the breather pipe, while the oil that has been separated from the blow-by gas within the oil separator is returned to the oil tank through an oil return pipe.
The oil containing a gas is returned to the oil tank by using a scavenging pump or the like, and the gas is separated from the returned oil and reserved within the oil tank. Therefore, the oil return pipe opens inside the oil tank at a location lower than a liquid level of the oil to inhibit backflow of the reserved gas. In the personal watercraft, the oil tank is elongate in the front-rear direction of the watercraft. In some cases, during starting, stopping, and acceleration or deceleration of the personal watercraft, the oil within the oil tank moves backward and forward due to inertia, and flows back from an opening of the oil return pipe toward the oil separator.